Counterbalanced pickup arm



Aug. 29, 1944. I L. THOMPSON ETAL 2,357,034

COUNTERBALANCED PICKUP ARM Filed Jfll 25, 1943 2 Sheets-Sheet 1 XNVENTOR L/A/couv THOMPSON Hebe/I L. SfqA/F y 9%? ATTORNEY Aug. 29, 1944- L. THOMPSON ET AL COUNTERBALANCED PICKUP ARM 2 Sheets-Sheet 2 Filed July 26, 1943 Patented Aug. 29, 1944 UNITED.

COUNTEBBALANCED PICKUI ARM mat. Thompson, Cheshire, and 1mm 1. Stone, Orange, Conn, assisnors to The Sonndscriber Corporation, New Haven. a co p ration of Connecticut Application July 2c. 1943, Serial No. 496.110

7 comm.

This invention relates to improvements in phonograph reproducing machines, and moreparticularly to a novel form of laterally counterbalanced reproducing arm which will permit the pickup needle to remain in its track and continue reproducing the record even when the machine is considerably oil-level.

The present invention is especially designed I for use with a phonograph reproducing from disk records havingclosely spaced relatively shallow indented or embossed grooves of the type disclosed in Reissue Patent No. 22,183, issued September 22, 1942, to Lincoln Thompson, and entitled Apparatus for recording sound on thin discs.

This application is a continuation in part of our prior co-pending application, Serial No. 492,- 246; filed June 25, 1943, entitled Spring hinge mountings for sound recording and reproducing heads.

One object of the present invention is to pro-' weight which is adapted to neutralize any lateral pickup-dislocating forces produced by tilting of the equipment to an oil-level position. The use of the present invention is of particular importance when the recording machine is used on mobile vehicles such as trucks or tanks, on shipboard, or on airplanes which frequently assume off-level positions.

A further object is to provide a dictating machine of the above nature, in which the dislocat ing forces tending to move the pickup needle out of the record grooves being reproduced will be completely compensated 'for so that the reproduction will not be interfered with even though direction and inclination.

A further object is to provide a counter-balanced reproducin arm of the above nature, in which the counter-balancing weight will bereadily adjustable with respect to the length of said arm.

A still further object of the present invention is to provide a reproducing arm of the above Fig. 1 represents a top plan view. of an improved disk record reproducing phonograph showing inf'ull lines a counter-balanced reproducing arm.

Fig. 2 is aside view of the reproducing arm as it'appears in use.

Fig. 3 is a plan view of the same.

Fig. 4 is a sectional view taken along the line 4-4 of Fig. 3, showing the construction of the pivotal mounting of the reproducing arm.

Fig. 5 is a rear view of the bearing bracket for the reproducing arm, showing the appearance of the improved wire tracking" spring which assists in holding the reproducing needle in its track.

Referring now to the drawings wherein like reference numerals denote corresponding parts throughout the several views, the numeral III ing the vehicle undergoes frequent changes in speed,

nature which will be relatively inexpensive to manufacture, simple in construction, compact, ornamental in appearance, and very eilicient and durable in use.

- With these and other objects in view there has been illustrated on the accompanying drawings one form in which the invention may be conveniently embodied in practice.

In the drawings,

dicates a rectangular cabinet, over which a tumtable II is adapted to be driven at constant speed by a suitable electric motor (not shown). The turntable H is provided with a vertical spindle I! having a square top [2a which serves to centralize a thin record tablet i3 mounted upon the turntable I I; and also to prevent slipping of said record on said turntable.

Areprcducing arm l'l, comprising the present invention, is mounted to swin in a horizontal plane when the machine is level) upon a vertical shaft I8, which is mounted on antifriction hearings in a U-shaped bearing bracket Ill. The bracket is has a horizontal base 19a adapted to be secured in a fixed position upon the cabinet to by means of a pair of screws I91), I921. The shaft IBis adapted to be connected rigidly to the reproducing arm H by means of a horizontal pin "a, a clearly shown in Fig. 4.

In order to neutralize the lateral component of the, force of gravity acting upon the pickup parallel to the record surface due to the weight of the reproducing arm l1 and the head 30 whenever the dictating machine is located in an oillevel positiomprovision is made of a rearwardiy extending upwardly-oifset auxiliary arm 20 connected to the rear portion of said reproducing arm II by screws 20a, 28a, and carrying upon its rear end a cylindrical counter-weight 2|, the axis of which ishorizontal and substantially in alignment with the longitudinal axis of the reproducing arm The auxiliary arm 20 is preferably made of still flat metal stock, and the rear end Ilaa of said arm 20 is adapted to be inserted within a thin horizontal slot Zia. which passes entirely through the upper portion of the counter-weight 2|, said arm 20 being locked in any desired position in said counter-weight II by means of a set screw 2| b.

Provision is also made of a light wire vertical "tracking" spring 22 which is adapted to be rig idly secured at its lower end to a rectangular plate 22a, attached, as by a lock screw 22b, to the lower portion of the rear surface of the U-shaped bearing bracket IS. The upper portion of the wire 22 extends loosely through a small aperture 220 formed in the upper offset portion 2041a of the-auxiliary arm 20. as clearly shown in Figs. 1, 2, 4, and 5.

The vertical shaft 18 is journaled at its upper end in a conical screw bearing 23 having a slotted end 230, said screw being locked in adJusted position by means of a nut 24 seated upon the top horizontal arm Man of the U-shaped bracket IS. The conical point 2412a of the screw bearing 23 is adapted to engage freely in a conical recess Iliad located in the top of the shaft II.

The bottom of the shaft I8 is provided with a vertical hinge pin 25, preferably consisting of a hardened drill rod which has a driving flt within a vertical cylindrical recess formed in the lower end of the shaft l8 (as shown in Fig. 4)

The lower end of the hinge pin 25 is adapted to rest upon a small ball bearing 26 located in a socket 21 formed in an upstanding boss 28, located on the base l9a of the U-shaped bearing bracket iii. The ball bearing 26 is adapted to be held detachably in operating position by means of a threaded cup-shaped ball retainer 29 screwed into said socket 21, said retainer preferably being constructed of along wearing material such as bronze.

The reproducing arm I! is provided at its forward end with the pickup head 30, connected to said arm I! as by a rectangular leaf spring hinge 3| (as clearly shown in Figs. 2 and 3).

In order to facilitate the lifting of the pickup head 30 from the record I3 whenever desired, provision is made of an upwardly inclined handle 33 detachably fastened to the forward end of said pickup head 30. The leaf spring hinge 3| isvsecured at its opposite ends to the reproducing arm I] and pickup head 30 as by screws 34, 35, 36, 31, as shown.

For the purpose of counter-balancing the weight of the pickup head 3. Provision is made, on the center portion of said pickup head 30, of an upstanding pin 38 which is connected by a helical coil 39 to an adjustable angle plate 40 having an elongated slot 4|, within which are located a pair of adjusting screws 42 and 43, as clearly shown in Fig. 2 of the drawings.

, While there has been disclosed in this specification one form in which the invention may be embodied, it is to be understood that this form is shown for the purpose of illustration only, and

2,357,084 I that the invention is not to be limited to the 898- cific disclosure but may be modified and embodied in various other forms without departing from the spirit. In short, the invention includes all the modifications and embodiments coming within the scope of the following claims.

Having thus fully described the invention what is claimed as new, and for which it is desired to secure Letters Patent, is:

1. In a phonograph, a driven turntable, a disk record supported thereon, a reproducing arm mounted to swing parallel to said record, the rear end of said arm being mounted on a bearing shaft located at right angles to said record, said 'arm having a counter-balancing weight adjustably secured thereto at a point behind said bouing shaft toneutralize the component of the force of gravity acting upon the reproducing needle parallel to the record surface tending to swing the reproducing head needle out of its groove when the phonograph is tilted to an oil-level position.

2. In a phonograph machine, a reproducing arm mounted to swing in a plane parallel to said record, a bearing shaft perpendicular to said record for supporting the rear end of said arm, a rearwardly extending auxiliary arm secured to the rear portion of said reproducing arm and extending rearwardly beyond said bearing shaft thereof, and a cylindrical counter-weight adjustably secured upon the rear end of said auxiliary arm to neutralize lateral needle dislocating forces due to gravity acting parallel to the record surface when the machine is tilted off-level.

3. The invention as set forth in claim 2 in which the counter-weight is located on substantially the same horizontal axis as said reproducing arm.

4. The invention as defined in claim 2, in which said auxiliary arm is constructed of thin fiat stiif material.

.5. The invention as set forth in claim 2, in which the rear portion of said auxiliary arm is secured to said counter-weight at a point above the center of said counter-weight.

6. In a phonograph, a. driven turntable, a disk record supported thereon, a reproducing arm mounted to swing parallel to said record, the rear end of said arm being mounted on a bearing shaft located at right angles to said record, said am having a counter-balancing weight secured thereto at a point behind said bearing shaft 'to neutralize any components of the force of gravity acting parallel to the surface of said record tending to swing the reproducing head needle out of its groove when the phonograph is tilted to an oil-level position.

. LINCOLN THOMPSON.

. ROBERT L. STONE. 

